CN113140224B - Apparatus and method for comfort noise generation mode selection - Google Patents
Apparatus and method for comfort noise generation mode selection Download PDFInfo
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Classifications
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- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10L—SPEECH ANALYSIS OR SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING; SPEECH OR AUDIO CODING OR DECODING
- G10L19/00—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis
- G10L19/012—Comfort noise or silence coding
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- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10L—SPEECH ANALYSIS OR SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING; SPEECH OR AUDIO CODING OR DECODING
- G10L19/00—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis
- G10L19/02—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis using spectral analysis, e.g. transform vocoders or subband vocoders
- G10L19/0204—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis using spectral analysis, e.g. transform vocoders or subband vocoders using subband decomposition
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- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10L—SPEECH ANALYSIS OR SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING; SPEECH OR AUDIO CODING OR DECODING
- G10L19/00—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis
- G10L19/04—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis using predictive techniques
- G10L19/16—Vocoder architecture
- G10L19/18—Vocoders using multiple modes
- G10L19/22—Mode decision, i.e. based on audio signal content versus external parameters
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- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10L—SPEECH ANALYSIS OR SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING; SPEECH OR AUDIO CODING OR DECODING
- G10L21/00—Processing of the speech or voice signal to produce another audible or non-audible signal, e.g. visual or tactile, in order to modify its quality or its intelligibility
- G10L21/02—Speech enhancement, e.g. noise reduction or echo cancellation
- G10L21/0208—Noise filtering
- G10L21/0216—Noise filtering characterised by the method used for estimating noise
- G10L21/0232—Processing in the frequency domain
Abstract
An apparatus for encoding audio information is provided. The apparatus for encoding audio information includes: a selector (110) for selecting a comfort noise generation mode from two or more comfort noise generation modes in dependence on a background noise characteristic of the audio input signal; and an encoding unit (120) for encoding the audio information, wherein the audio information comprises mode information indicating the selected comfort noise generation mode.
Description
The present application is a divisional application of a chinese invention patent application "apparatus and method for comfort noise generation mode selection" with application number 201580040583.3, day 2015, month 7 and day 16.
Technical Field
The present invention relates to audio signal encoding, processing and decoding, and in particular to an apparatus and method for comfort noise generation mode selection.
Background
Communication speech and audio codecs (e.g., AMR-WB, g.718) typically include Discontinuous Transmission (DTX) mechanisms and Comfort Noise Generation (CNG) algorithms. DTX/CNG operation is used to reduce the transmission rate by modeling background noise during periods of inactive signals.
CNG may be implemented in several ways, for example.
The most common methods, such as those employed in the codecs of AMR-WB (ITU-T g.722.2 annex a) and g.718 (ITU-T g.718 sections 6.12 and 7.12), are based on the excitation + Linear Prediction (LP) model. The random excitation signal is first generated, then scaled by gain, and finally synthesized using an LP inverse filter, thereby generating a time domain CNG signal. The two main parameters that are transmitted are excitation energy and LP coefficients (usually expressed using LSF or ISF). This process is referred to herein as LP-CNG.
Another approach, which is based on a Frequency Domain (FD) representation of the background noise, has been recently proposed and described, for example, in patent application WO2014/096279"Generation of a comfort noise with high spectro-temporal resolution in discontinuous transmission of audio signals". Random noise is generated (e.g., FFT, MDCT, QMF) in the frequency domain, then shaped using FD representation of background noise, and finally converted from the frequency domain to the time domain, thereby generating a time domain CNG signal. The two main parameters that are transmitted are the global gain and a set of band noise levels. This process is referred to herein as FD-CNG.
Disclosure of Invention
It is an object of the present invention to provide an improved concept for comfort noise generation. The object of the invention is solved by an apparatus according to claim 1, an apparatus according to claim 10, a system according to claim 13, a method according to claim 14, a method according to claim 15, a computer program according to claim 16.
An apparatus for encoding audio information is provided. The apparatus for encoding audio information includes: a selector for selecting a comfort noise generation mode from two or more comfort noise generation modes according to a background noise characteristic of an audio input signal; and an encoding unit configured to encode the audio information, wherein the audio information includes mode information indicating the selected comfort noise generation mode.
In particular, the examples are based on the following findings: FD-CNG gives better quality for highly inclined background noise signals (e.g. car noise); while LP-CNG gives better quality for spectrally flatter background noise signals (office noise).
To obtain the best possible quality from a DTX/CNG system, according to an embodiment, both CNG methods are used, and one of them is selected according to the background noise characteristics.
Embodiments provide a selector that decides which CNG mode, such as LP-CNG or FD-CNG, should be used.
According to an embodiment, the selector may be configured, for example, to: the tilt of the background noise of the audio input signal is determined as a background noise characteristic. The selector may, for example, be configured to: the comfort noise generation mode is selected from two or more comfort noise generation modes according to the determined tilt.
In an embodiment, the apparatus may for example further comprise a noise estimator for estimating per-band estimates of background noise for each of the plurality of frequency bands. The selector may for example be configured to determine the tilt from estimated background noise of the plurality of frequency bands.
According to an embodiment, the noise estimator may be configured, for example, to: a per-band estimate of background noise is estimated by estimating the energy of the background noise for each of a plurality of frequency bands.
In an embodiment, the noise estimator may be configured, for example, to: a low frequency background noise value indicative of a first background noise energy of a first set of the plurality of frequency bands is determined from per-band estimates of background noise of each of the first set of the plurality of frequency bands.
Also, in such embodiments, the noise estimator may be configured, for example, to: a high frequency background noise value indicative of second background noise energy of a second set of the plurality of frequency bands is determined from per-band estimates of background noise of each of the second set of the plurality of frequency bands. At least one frequency band in the first set may, for example, have a center frequency that is lower than a center frequency of at least one frequency band in the second set. In particular embodiments, each frequency band of the first set may, for example, have a center frequency that is lower than a center frequency of each frequency band of the second set.
Further, the selector may be configured, for example, to: the tilt is determined based on the low frequency background noise value and the high frequency background noise value.
According to an embodiment, the noise estimator may be configured to determine the low frequency background noise value L as follows:
where i represents the ith band in the first set of bands, 1 1 Representing a first frequency band of the plurality of frequency bands, I 2 Representing a second frequency band of the plurality of frequency bands, and N [ i ]]An energy estimate representing background noise energy for the i-th frequency band.
In an embodiment, the noise estimator may be configured to determine the high frequency background noise value H, for example, according to the following equation:
wherein I represents the ith band in the second set of bands, I 3 Representing a third frequency band of the plurality of frequency bands, I 4 Represents a fourth frequency band of the plurality of frequency bands, and N [ i ]]An energy estimate representing background noise energy for the i-th frequency band.
According to an embodiment, the selector may be configured, for example, to:
according to the formulaOr alternatively
According to the formulaOr alternatively
According to the formula t=l-H, or
According to the formula t=h-L,
the tilt T is determined from the low frequency background noise value L and the high frequency background noise value H.
In an embodiment, the selector may be configured to determine the tilt as a current short-term tilt value, for example. Moreover, the selector may be configured to determine the current long-term tilt value from the current short-term tilt value and a previous long-term tilt value, for example. Further, the selector may be configured to select one of the two or more comfort noise generation modes in accordance with the current long-term tilt value, for example.
According to an embodiment, the selector may be configured, for example, to determine the current long-term tilt value T according to the following formula cLT ：
T cLT ＝αT pLT +(1-α)T，
Wherein T is the current short-term tilt value, T pLT Is the previous long-term tilt value, and α is a real number, and 0 < α < 1.
In an embodiment, a first one of the two or more comfort noise generation modes may be, for example, a frequency domain comfort noise generation mode. Also, a second of the two or more comfort noise generation modes may be, for example, a linear prediction domain comfort noise generation mode. Further, the selector may be configured, for example, to: the frequency domain comfort noise generation mode is selected if the previously selected generation mode (previously selected by the selector) is a linear prediction domain comfort noise generation mode and the current long term tilt value is greater than a first threshold. Moreover, the selector may be configured, for example, to: if the previously selected generation mode (previously selected by the selector) is a frequency domain comfort noise generation mode and the current long-term tilt value is less than the second threshold, a linear prediction domain comfort noise generation mode is selected.
Also, an apparatus for generating an audio output signal based on received encoded audio information is provided. The device comprises: a decoding unit for decoding encoded audio information to obtain mode information encoded within the encoded audio information, wherein the mode information indicates an indicated comfort noise generation mode of the two or more comfort noise generation modes. Moreover, the apparatus includes: a signal processor for generating the audio output signal by generating comfort noise according to the indicated comfort noise generation mode.
According to an embodiment, a first one of the two or more comfort noise generation modes may be, for example, a frequency domain comfort noise generation mode. The signal processor may, for example, be configured to: if the indicated comfort noise generation mode is a frequency domain comfort noise generation mode, comfort noise is generated in a frequency domain and the comfort noise generated in the frequency domain is frequency-to-time converted. For example, in particular embodiments, the signal processor may be configured, for example, to: if the indicated comfort noise generation mode is a frequency domain comfort noise generation mode, comfort noise is generated by generating random noise in the frequency domain, shaping the random noise in the frequency domain to obtain shaped noise, and converting the shaped noise from the frequency domain to the time domain.
In an embodiment, the second of the two or more comfort noise generation modes may be, for example, a linear prediction domain comfort noise generation mode. The signal processor may, for example, be configured to: if the indicated comfort noise generation mode is a linear prediction domain comfort noise generation mode, the comfort noise is generated by using a linear prediction filter. For example, in particular embodiments, the signal processor may be configured, for example, to: if the indicated comfort noise generation mode is a linear prediction domain comfort noise generation mode, comfort noise is generated by generating a random excitation signal, scaling the random excitation signal to obtain a scaled excitation signal, and synthesizing the scaled excitation signal using an LP inverse filter.
Furthermore, a system is provided. The system comprises: the apparatus for encoding audio information according to one of the above embodiments, the apparatus for generating an audio output signal based on the received encoded audio information according to one of the above embodiments. The selector of the means for encoding audio information is configured to: a comfort noise generation mode is selected from two or more comfort noise generation modes based on a background noise characteristic of the audio input signal. The encoding unit of the apparatus for encoding audio information is configured to: the audio information is encoded to obtain encoded audio information, wherein the audio information includes mode information indicating the selected comfort noise generation mode as the indicated comfort noise generation mode. Also, the decoding unit of the means for generating an audio output signal is configured to receive the encoded audio information and is further configured to decode the encoded audio information to obtain mode information encoded within the encoded audio information. The signal processor of the means for generating an audio output signal is configured to: the audio output signal is generated by generating comfort noise according to the indicated comfort noise generation mode.
Also, a method for encoding audio information is provided. The method comprises the following steps:
-selecting a comfort noise generation mode from two or more comfort noise generation modes depending on a background noise characteristic of the audio input signal; and
-encoding the audio information, wherein the audio information comprises mode information indicating the selected comfort noise generation mode.
Furthermore, a method for generating an audio output signal based on received encoded audio information is provided. The method comprises the following steps:
-decoding the encoded audio information to obtain mode information encoded within the encoded audio information, wherein the mode information indicates an indicated comfort noise generation mode of two or more comfort noise generation modes, and
-generating the audio output signal by generating comfort noise according to the indicated comfort noise generation mode.
Furthermore, a computer program for implementing the above method when executed on a computer or signal processor is provided.
Thus, in some embodiments, the proposed selector may be based, for example, on the tilt of the background noise. For example, if the slope of the background noise is high, FD-CNG is selected, otherwise LP-CNG is selected.
A smoothed version of the background noise tilt and hysteresis may be used, for example, to avoid frequent switching from one mode to another.
The tilt of the background noise may be estimated, for example, using a ratio of low frequency background noise energy and high frequency background noise energy.
Background noise energy may be estimated in the frequency domain, for example, using a noise estimator.
Drawings
Embodiments of the present invention will be described in more detail below with reference to the attached drawing figures, wherein:
figure 1 shows an apparatus for encoding audio information according to an embodiment,
figure 2 shows an apparatus for encoding audio information according to another embodiment,
figure 3 illustrates a stepwise method for selecting a comfort noise generation mode according to an embodiment,
FIG. 4 illustrates an apparatus for generating an audio output signal based on received encoded audio information, in accordance with an embodiment, an
Fig. 5 shows a system according to an embodiment.
Detailed Description
Fig. 1 shows an apparatus for encoding audio information according to an embodiment.
The apparatus for encoding audio information includes: a selector 110 for selecting a comfort noise generation mode from two or more comfort noise generation modes according to a background noise characteristic of the audio input signal.
Moreover, the apparatus includes: an encoding unit 120 for encoding audio information, wherein the audio information comprises mode information indicating the selected comfort noise generation mode.
For example, a first of the two or more comfort noise generation modes may be, for example, a frequency domain comfort noise generation mode. And/or, for example, a second of the two or more generation modes may be, for example, a linear prediction domain comfort noise generation mode.
For example, if encoded audio information is received at the decoder side, wherein the mode information encoded within the encoded audio information indicates that the selected comfort noise generation mode is a frequency domain comfort noise generation mode, the signal processor at the decoder side may generate comfort noise, for example, by: generating random noise in the frequency domain, shaping the random noise in the frequency domain to obtain shaped noise, and converting the shaped noise from the frequency domain to the time domain.
However, if the mode information encoded within the encoded audio information indicates that the selected comfort noise generation mode is a linear prediction domain comfort noise generation mode, for example, the signal processor at the decoder side may generate comfort noise, for example, by: generating a random excitation signal, scaling the random excitation signal to obtain a scaled excitation signal, and synthesizing the scaled excitation signal using an LP inverse filter.
Within the encoded audio information, not only information about the comfort noise generation mode but also additional information may be encoded. For example, band-specific gain factors may also be encoded, e.g., where one gain factor is encoded for each band. Alternatively, for example, one or more LP filter coefficients or LSF coefficients or ISF coefficients may be encoded within the encoded audio information. The information about the selected comfort noise generation mode and the additional information encoded in the encoded audio information may then be transmitted to the decoder side, for example in SID frames (sid=silence insertion descriptor).
Information about the selected comfort noise generation mode may be explicitly encoded or implicitly encoded.
When explicitly encoding the selected comfort noise generation mode, one or more bits may be used, for example, to indicate which of the two or more comfort noise generation modes the selected comfort noise generation mode is. In such an embodiment, the one or more bits are then encoded mode information.
However, in other embodiments, the selected comfort noise generation mode is implicitly encoded within the audio information. For example, in the above examples, the band-specific gain factor and one or more LP (or LSF or ISF) may, for example, have different data formats, or may, for example, have different bit lengths. For example, if a band-specific gain factor is encoded within the audio information, this may for example indicate that the frequency domain comfort noise generation mode is the selected comfort noise generation mode. However, if one or more LP (or LSF or ISF) coefficients are encoded within the audio information, this may, for example, indicate that the linear prediction domain comfort noise generation mode is the selected comfort noise generation mode. When such implicit coding is used, the band-specific gain factor or one or more LP (or LSF or ISF) coefficients then represent mode information encoded within the encoded audio signal, wherein the mode information indicates the selected comfort noise generation mode.
According to an embodiment, the selector 110 may for example be configured to determine a tilt of the background noise of the audio input signal as the background noise characteristic. The selector 110 may, for example, be configured to: the comfort noise generation mode is selected from two or more comfort noise generation modes according to the determined tilt.
For example, a low frequency background noise value and a high frequency background noise value may be utilized, and the tilt of the background noise may be calculated, for example, from the low frequency background noise value and the high frequency background noise value.
Fig. 2 shows an apparatus for encoding audio information according to another embodiment. The apparatus of fig. 2 further comprises: a noise estimator 105 for estimating a per-band estimate of the background noise for each of the plurality of frequency bands. The selector 110 may, for example, be configured to determine the tilt from estimated background noise of the plurality of frequency bands.
According to an embodiment, the noise estimator 105 may be configured, for example, to: a per-band estimate of background noise is estimated by estimating the energy of the background noise for each of a plurality of frequency bands.
In an embodiment, the noise estimator 105 may be configured, for example, to: a low frequency background noise value indicative of a first background noise energy of a first set of the plurality of frequency bands is determined from per-band estimates of background noise of each of the first set of the plurality of frequency bands.
Moreover, the noise estimator 105 may be configured to, for example: a high frequency background noise value indicative of second background noise energy of a second set of the plurality of frequency bands is determined from per-band estimates of background noise of each of the second set of the plurality of frequency bands. At least one frequency band in the first set may, for example, have a center frequency that is lower than a center frequency of at least one frequency band in the second set. In particular embodiments, each frequency band of the first set may, for example, have a center frequency that is lower than a center frequency of each frequency band of the second set.
Further, the selector 110 may be configured to, for example: the tilt is determined based on the low frequency background noise value and the high frequency background noise value.
According to an embodiment, the noise estimator 105 may for example be configured to determine the low frequency background noise value L according to the following formula:
wherein I represents the ith band in the first set of bands, I 1 Representing a first frequency band of the plurality of frequency bands, I 2 Representing a second frequency band of the plurality of frequency bands, and N [ i ]]An energy estimate representing background noise energy for the i-th frequency band.
Similarly, in an embodiment, the noise estimator 105 may be configured to determine the high frequency background noise value H, for example, according to the following equation:
Wherein I represents the ith band in the second set of bands, I 3 Representing a third frequency band of the plurality of frequency bands, I 4 Represents a fourth frequency band of the plurality of frequency bands, and N [ i ]]An energy estimate representing background noise energy for the i-th frequency band.
According to an embodiment, the selector 110 may be configured, for example, to:
according to the formulaOr alternatively
According to the formulaOr alternatively
According to the formula t=l-H, or
According to the formula t=h-L,
the tilt T is determined from the low frequency background noise value L and the high frequency background noise value H.
For example, when L and H are represented in the logarithmic domain, one of the subtraction formulas (t=l-H or t=h-L) may be employed.
In an embodiment, the selector 110 may be configured, for example, to: the tilt is determined as the current short-term tilt value. Moreover, the selector 110 may be configured to determine the current long-term tilt value from the current short-term tilt value and a previous long-term tilt value, for example. Further, the selector 110 may be configured to select one of two or more comfort noise generation modes, for example, according to the current long-term tilt value.
According to an embodiment, the selector 110 may be configured, for example, to determine the current long-term tilt value T according to the following formula cLT ：
T cLT ＝αT pLT +(1-α)T，
Wherein T is the current short-term tilt value, T pLT Is the previous long-term tilt value, and α is a real number, and 0 < α < 1.
In an embodiment, a first one of the two or more comfort noise generation modes may be, for example, a frequency domain comfort noise generation mode FD CNG. Also, a second of the two or more comfort noise generation modes may be, for example, a linear prediction domain comfort noise generation mode, LP CNG. Further, the selector 110 may be configured to, for example: if the previously selected generation mode cng_mode_prev (previously selected by the selector 110) is the linear prediction domain comfort noise generation mode LP CNG and the current long term tilt value is greater than the first threshold thr 1 Then the frequency domain comfort noise generation mode FD CNG is selected. WhileAnd, the selector 110 may be configured, for example, to: if the previously selected generation mode cng_mode_prev (previously selected by the selector 110) is the frequency domain comfort noise generation mode fd_cng and the current long-term tilt value is less than the second threshold thr 2 Then the linear prediction domain comfort noise generation mode FD CNG is selected.
In some embodiments, the first threshold is equal to the second threshold. However, in other embodiments, the first threshold is not equal to the second threshold.
Fig. 4 shows an apparatus for generating an audio output signal based on received encoded audio information according to an embodiment.
The device comprises: a decoding unit 210 for decoding the encoded audio information to obtain mode information encoded within the encoded audio information. The mode information indicates the indicated comfort noise generation mode of the two or more comfort noise generation modes.
Moreover, the apparatus includes: a signal processor 220 for generating an audio output signal by generating comfort noise according to the indicated comfort noise generation mode.
According to an embodiment, a first of the two or more comfort noise generation modes may be, for example, a frequency domain comfort noise generation mode. The signal processor 220 may, for example, be configured to: if the indicated comfort noise generation mode is a frequency domain comfort noise generation mode, comfort noise is generated in a frequency domain and the comfort noise generated in the frequency domain is frequency-to-time converted. For example, in particular embodiments, the signal processor may be configured, for example, to: if the indicated comfort noise generation mode is a frequency domain comfort noise generation mode, comfort noise is generated by generating random noise in the frequency domain, shaping the random noise in the frequency domain to obtain shaped noise, and converting the shaped noise from the frequency domain to the time domain.
For example, the concepts described in WO 2014/096279 A1 may be employed.
For example, a random generator may be applied to excite each individual spectral band in the FFT domain and/or QMF (FFT = fast fourier transform; QMF = quadrature mirror filter) domain by generating one or more random sequences. The shaping of the random noise may be performed, for example, by separately calculating the amplitude of the random sequence in each frequency band such that the spectrum of the generated comfort noise resembles the spectrum of the actual background noise present, for example, in a bitstream comprising, for example, the audio input signal. Thus, for example, the calculated amplitude may be applied to a random sequence, for example by multiplying the random sequence with the calculated amplitude in each frequency band. Then, conversion of the shaped noise from the frequency domain to the time domain may be employed.
In an embodiment, the second of the two or more comfort noise generation modes may be, for example, a linear prediction domain comfort noise generation mode. The signal processor 220 may, for example, be configured to: if the indicated comfort noise generation mode is a linear prediction domain comfort noise generation mode, the comfort noise is generated by using a linear prediction filter. For example, in particular embodiments, the signal processor may be configured, for example, to: if the indicated comfort noise generation mode is a linear prediction domain comfort noise generation mode, comfort noise is generated by generating a random excitation signal, scaling the random excitation signal to obtain a scaled excitation signal, and synthesizing the scaled excitation signal using an LP inverse filter.
For example, comfort noise generation as described in g.722.2 (see ITU-T g.722.2 annex a) and/or g.718 (see ITU-T g.718 sections 6.12 and 7.12) may be employed. Comfort noise generation in this random excitation domain, which is achieved by scaling the random excitation signal to obtain a scaled excitation signal and synthesizing the scaled excitation signal using an LP inverse filter, is well known to those skilled in the art.
Fig. 5 shows a system according to an embodiment. The system comprises: the apparatus 100 for encoding audio information according to one of the above-described embodiments; and an apparatus 200 for generating an audio output signal based on the received encoded audio information according to one of the above-described embodiments.
The selector 110 of the apparatus 100 for encoding audio information is configured to: a comfort noise generation mode is selected from two or more comfort noise generation modes based on a background noise characteristic of the audio input signal. The encoding unit 120 of the apparatus 100 for encoding audio information is configured to: the audio information is encoded to obtain encoded audio information, wherein the audio information includes mode information indicating the selected comfort noise generation mode as the indicated comfort noise generation mode.
Also, the decoding unit 210 of the apparatus 200 for generating an audio output signal is configured to receive encoded audio information and is further configured to decode the encoded audio information to obtain mode information encoded within the encoded audio information. The signal processor 220 of the apparatus 200 for generating an audio output signal is configured to: an audio output signal is generated by generating comfort noise according to the indicated comfort noise generation mode.
Fig. 3 illustrates a stepwise method for selecting a comfort noise generation mode according to an embodiment.
In step 310, a noise estimator is used to estimate background noise energy in the frequency domain. This is typically performed on a per band basis, resulting in an energy estimate per band N i, where 0.ltoreq.i < N and N is the number of bands (e.g., n=20).
Any noise estimator that produces an estimate of background noise energy per band may be used. One example is a noise estimator used in g.718 (ITU-T g.718 section 6.7).
In step 320, background noise energy in the low frequency is calculated using the following equation:
wherein I is 1 And I 2 May depend on signal bandwidth, e.g. for NB, I 1 ＝1，I 2 =9, and for WB, I 1 ＝0，I 2 ＝10。
L may be regarded as the low frequency background noise value described above.
In step 330, the background noise energy in the high frequency is calculated using the following equation:
wherein I is 3 And I 4 May depend on signal bandwidth, e.g. for NB, I 3 ＝16，I 4 =17 and for WB, I 3 ＝19，I 4 ＝20。
H may be regarded as the high frequency background noise value described above.
Steps 320 and 330 may be performed, for example, subsequently or independently of each other.
In step 340, the background noise tilt is calculated using the following
Some embodiments may proceed, for example, according to step 350. In step 350, the background noise tilt is smoothed to produce a long-term version T of the background noise tilt LT ＝αT LT +(1-α)T
Where α is, for example, 0.9. In the recursive equation, T to the left of the equal sign LT Is the current long-term tilt value T mentioned above cLT While T on the right side of the equal sign LT Is the previous long-term tilt value T mentioned above pLT 。
In step 360, the CNG mode is finally selected using the following classifier with hysteresis:
If(cng_mode_prev＝＝LP_CNG andT LT ＞thr 1 )then cng_mode＝FD_CNG
If(cng_mode_prev＝＝FD_CNG andT LT ＜thr 2 )then cng_mode＝LP_CNG
wherein thr 1 And thr 2 May depend on bandwidth, e.g., thr for NB 1 ＝9，thr 2 =2, for WB thr 1 ＝45，thr 2 ＝10。
cng_mode is the comfort noise generation mode (currently) selected by the selector 110.
cng_mode_prev is a previously selected (comfort noise) generation mode that selector 110 has previously selected.
What happens when any of the above conditions in step 360 are not met will depend on the implementation. In one embodiment, for example, if either of the two conditions in step 360 is not met, the CNG mode may remain the same as it was, such that
cng_mode＝cng_mode_prev。
Other embodiments may implement other selection strategies.
In the embodiment of FIG. 3, thr 1 Not equal to thr 2 However, in other embodiments thr 1 Equal to thr 2 。
The invention may be further implemented by the following embodiments, which may be combined with any of the examples and embodiments described and claimed herein:
1. an apparatus for encoding audio information, comprising:
a selector (110) for selecting a comfort noise generation mode from two or more comfort noise generation modes in dependence on a background noise characteristic of the audio input signal; and
an encoding unit (120) for encoding the audio information, wherein the audio information comprises mode information indicating the selected comfort noise generation mode,
wherein a first of the two or more comfort noise generation modes is a frequency domain comfort noise generation mode and the frequency domain comfort noise generation mode indicates: the comfort noise should be generated in a frequency domain, and the comfort noise generated in the frequency domain should be performed frequency-to-time conversion.
2. According to the apparatus of the embodiment 1,
wherein the selector (110) is configured to: determining a tilt of a background noise of the audio input signal as the background noise characteristic; and
Wherein the selector (110) is configured to: the comfort noise generation mode is selected from two or more comfort noise generation modes according to the determined tilt.
3. According to the apparatus of the embodiment 2,
wherein the apparatus further comprises: a noise estimator (105) for estimating per-band estimates of the background noise for each of a plurality of frequency bands; and
wherein the selector (110) is configured to determine the tilt from estimated background noise of the plurality of frequency bands.
4. According to the apparatus of the embodiment 3,
wherein the noise estimator (105) is configured to: determining a low frequency background noise value indicative of a first background noise energy of a first set of the plurality of frequency bands from per-band estimates of background noise of each of the first set of the plurality of frequency bands,
wherein the noise estimator (105) is configured to: determining a high frequency background noise value indicative of a second background noise energy of a second set of the plurality of frequency bands from per-band estimates of the background noise of each of the second set of the plurality of frequency bands, wherein at least one frequency band of the first set has a center frequency lower than a center frequency of at least one frequency band of the second set, an
Wherein the selector (110) is configured to: the tilt is determined from the low frequency background noise value and the high frequency background noise value.
5. According to the apparatus of the embodiment 4,
wherein the noise estimator (105) is configured to determine the low frequency background noise value L according to:
wherein I represents the ith band in the first set of bands, I 1 Representing a first frequency band of the plurality of frequency bands, I 2 Representing the multipleA second one of the frequency bands and N [ i ]]An energy estimate representing background noise energy for the i-th frequency band,
wherein the noise estimator (105) is configured to determine the high frequency background noise value H according to:
wherein I represents the ith band in the second set of bands, I 3 Representing a third frequency band of the plurality of frequency bands, I 4 Represents a fourth frequency band of the plurality of frequency bands, and N [ i ]]An energy estimate representing background noise energy for the i-th frequency band.
6. According to the apparatus of the embodiment 4,
wherein the selector (110) is configured to:
according to the formulaOr alternatively
According to the formulaOr alternatively
According to the formula t=l-H, or
According to the formula t=h-L,
the tilt T is determined from the low frequency background noise value L and the high frequency background noise value H.
7. According to the apparatus of the embodiment 2,
wherein the selector (110) is configured to determine the tilt as a current short-term tilt value (T),
wherein the selector (110) is configured to determine a current long-term tilt value from a current short-term tilt value and a previous long-term tilt value,
wherein the selector (110) is configured to select one of two or more comfort noise generation modes depending on the current long-term tilt value.
8. According to the apparatus of the embodiment 7,
wherein the selector (110) is configured to determine the current long-term tilt value T according to the following formula cLT ：
T cLT ＝αT pLT +(1-α)T，
Wherein the method comprises the steps of
T is the current short-term tilt value,
T pLT is the previous long-term tilt value
Alpha is a real number and 0 < alpha < 1.
9. According to the apparatus of the embodiment 7,
wherein a first of the two or more comfort noise generation modes is a frequency domain comfort noise generation mode,
wherein a second of the two or more comfort noise generation modes is a linear prediction domain comfort noise generation mode,
wherein the selector (110) is configured to: if the previously selected generation mode is a linear prediction domain comfort noise generation mode and the current long term tilt value is greater than a first threshold, selecting a frequency domain comfort noise generation mode, wherein the previously selected generation mode was previously selected by the selector (110), and
Wherein the selector (110) is configured to: if the previously selected generation mode is a frequency domain comfort noise generation mode and the current long term tilt value is less than a second threshold, a linear prediction domain comfort noise generation mode is selected, wherein the previously selected generation mode was previously selected by the selector (110).
10. An apparatus for generating an audio output signal based on received encoded audio information, comprising:
a decoding unit (210) for decoding encoded audio information to obtain mode information encoded within the encoded audio information, wherein the mode information indicates an indicated comfort noise generation mode of two or more comfort noise generation modes; and
a signal processor (220) for generating the audio output signal by generating comfort noise according to the indicated comfort noise generation mode,
wherein a first of the two or more comfort noise generation modes is a frequency domain comfort noise generation mode, and
wherein the signal processor is configured to: if the indicated comfort noise generation mode is a frequency domain comfort noise generation mode, comfort noise is generated in a frequency domain and the comfort noise generated in the frequency domain is frequency-to-time converted.
11. According to the apparatus of embodiment 10,
wherein a second of the two or more comfort noise generation modes is a linear prediction domain comfort noise generation mode, an
Wherein the signal processor (220) is configured to: if the indicated comfort noise generation mode is a linear prediction domain comfort noise generation mode, the comfort noise is generated by using a linear prediction filter.
12. A system, comprising:
the apparatus (100) for encoding audio information according to one of embodiments 1 to 9,
the apparatus (200) for generating an audio output signal based on received encoded audio information according to embodiment 10 or 11,
wherein the selector (110) of the apparatus (100) according to one of embodiments 1 to 9 is configured to: a comfort noise generation mode is selected from two or more comfort noise generation modes based on a background noise characteristic of the audio input signal,
the encoding unit (120) of the apparatus (100) according to one of embodiments 1 to 9 is configured to: encoding the audio information to obtain encoded audio information, wherein the audio information comprises mode information indicating the selected comfort noise generation mode as the indicated comfort noise generation mode,
Wherein the decoding unit (210) of the apparatus (200) according to embodiment 10 or 11 is configured to receive the encoded audio information and is further configured to decode the encoded audio information to obtain mode information encoded within the encoded audio information, and
wherein the signal processor (220) of the apparatus (200) according to embodiment 10 or 11 is configured to: the audio output signal is generated by generating comfort noise according to the indicated comfort noise generation mode.
13. A method for encoding audio information, comprising:
selecting a comfort noise generation mode from two or more comfort noise generation modes according to a background noise characteristic of the audio input signal; and
encoding the audio information, wherein the audio information includes mode information indicating a selected comfort noise generation mode,
wherein a first of the two or more comfort noise generation modes is a frequency domain comfort noise generation mode and the frequency domain comfort noise generation mode indicates: the comfort noise should be generated in a frequency domain, and the comfort noise generated in the frequency domain should be performed frequency-to-time conversion.
14. A method for generating an audio output signal based on received encoded audio information, comprising:
decoding the encoded audio information to obtain mode information encoded within the encoded audio information, wherein the mode information indicates an indicated comfort noise generation mode of two or more comfort noise generation modes, and
generating the audio output signal by generating comfort noise according to the indicated comfort noise generation mode,
wherein a first of the two or more comfort noise generation modes is a frequency domain comfort noise generation mode, and
wherein the signal processor is configured to: if the indicated comfort noise generation mode is a frequency domain comfort noise generation mode, comfort noise is generated in a frequency domain and the comfort noise generated in the frequency domain is frequency-to-time converted.
15. A computer readable medium storing a computer program for implementing the method according to embodiment 13 or 14 when executed on a computer or signal processor.
Although some aspects have been described in the context of apparatus, it will be clear that these aspects also represent a description of the respective method, wherein a block or device corresponds to a method step or a feature of a method step. Similarly, the approaches described in the context of method steps also represent descriptions of features of corresponding blocks or items or corresponding devices.
The novel deconstructed signal may be stored on a digital storage medium or may be transmitted over a transmission medium such as a wireless transmission medium or a wired transmission medium (e.g., the internet).
Embodiments of the invention may be implemented in hardware or in software, depending on certain implementation requirements. The implementation can be performed using a digital storage medium (e.g., floppy disk, DVD, CD, ROM, PROM, EPROM, EEPROM, or flash memory) having stored thereon electronically readable control signals, which cooperate (or are capable of cooperating) with a programmable computer system such that the corresponding method is performed.
Some embodiments according to the invention comprise a non-transitory data carrier having electronically readable control signals capable of cooperating with a programmable computer system to perform one of the methods described herein.
In general, embodiments of the invention may be implemented as a computer program product having a program code operable to perform one of the methods when the computer program product is run on a computer. The program code may for example be stored on a machine readable carrier.
Other embodiments include a computer program stored on a machine-readable carrier for performing one of the methods described herein.
In other words, an embodiment of the inventive method is thus a computer program with a program code for performing one of the methods described herein when the computer program runs on a computer.
Thus, another embodiment of the inventive method is a data carrier (or digital storage medium or computer readable medium) having a computer program recorded thereon for performing one of the methods described herein.
Thus, another embodiment of the inventive method is a data stream or signal sequence representing a computer program for performing one of the methods described herein. The data stream or signal sequence may, for example, be configured to be transmitted via a data communication connection (e.g., via the internet).
Another embodiment includes a processing device, such as a computer or programmable logic device, configured or adapted to perform one of the methods described herein.
Another embodiment includes a computer having a computer program installed thereon for performing one of the methods described herein.
In some embodiments, a programmable logic device (e.g., a field programmable gate array) may be used to perform some or all of the functions of the methods described herein. In some embodiments, a field programmable gate array may cooperate with a microprocessor to perform one of the methods described herein. In general, the method is preferably performed by any hardware device.
The above-described embodiments are merely illustrative of the principles of the present invention. It should be understood that: modifications and variations of the arrangements and details described herein will be apparent to other persons skilled in the art. It is therefore intended that the scope of the appended patent claims be limited only and not by the specific details given by way of description and explanation of the embodiments herein.
Claims (15)
1. An apparatus for encoding audio information, comprising:
a selector (110) for selecting a comfort noise generation mode from two or more comfort noise generation modes in dependence on a background noise characteristic of the audio input signal; and
an encoding unit (120) for encoding the audio information, wherein the audio information comprises mode information indicating the selected comfort noise generation mode,
wherein a first of the two or more comfort noise generation modes is a frequency domain comfort noise generation mode.
2. The device according to claim 1,
wherein the selector (110) is configured to: determining a tilt of a background noise of the audio input signal as the background noise characteristic; and
wherein the selector (110) is configured to: the comfort noise generation mode is selected from two or more comfort noise generation modes according to the determined tilt.
3. The device according to claim 2,
wherein the apparatus further comprises: a noise estimator (105) for estimating per-band estimates of the background noise for each of a plurality of frequency bands; and
wherein the selector (110) is configured to determine the tilt from estimated background noise of the plurality of frequency bands.
4. A device according to claim 3,
wherein the noise estimator (105) is configured to: determining a low frequency background noise value indicative of a first background noise energy of a first set of the plurality of frequency bands from per-band estimates of background noise of each of the first set of the plurality of frequency bands,
wherein the noise estimator (105) is configured to: determining a high frequency background noise value indicative of a second background noise energy of a second set of the plurality of frequency bands from per-band estimates of the background noise of each of the second set of the plurality of frequency bands, wherein at least one frequency band of the first set has a center frequency lower than a center frequency of at least one frequency band of the second set, an
Wherein the selector (110) is configured to: the tilt is determined from the low frequency background noise value and the high frequency background noise value.
5. The device according to claim 4,
wherein the noise estimator (105) is configured to determine the low frequency background noise value L according to:
wherein I represents the ith band in the first set of bands, I 1 Representing a first frequency band of the plurality of frequency bands, I 2 Representing a second frequency band of the plurality of frequency bands, and N [ i ]]An energy estimate representing background noise energy for the i-th frequency band,
wherein the noise estimator (105) is configured to determine the high frequency background noise value H according to:
wherein I represents the ith band in the second set of bands, I 3 Representing a third frequency band of the plurality of frequency bands, I 4 Represents a fourth frequency band of the plurality of frequency bands, and N [ i ]]An energy estimate representing background noise energy for the i-th frequency band.
6. The device according to claim 4,
wherein the selector (110) is configured to:
according to the formulaOr alternatively
According to the formulaOr alternatively
According to the formula t=l-H, or
According to the formula t=h-L,
the tilt T is determined from the low frequency background noise value L and the high frequency background noise value H.
7. The device according to claim 2,
wherein the selector (110) is configured to determine the tilt as a current short-term tilt value (T),
Wherein the selector (110) is configured to determine a current long-term tilt value from a current short-term tilt value and a previous long-term tilt value,
wherein the selector (110) is configured to select one of two or more comfort noise generation modes depending on the current long-term tilt value.
8. The device according to claim 7,
wherein the selector (110) is configured to determine the current long-term tilt value T according to the following formula cLT ：
T cLT ＝αT pLT +(1–α)T,
Wherein the method comprises the steps of
T is the current short-term tilt value,
T pLT is the previous long-term tilt value
α is a real number, and 0< α <1.
9. The device according to claim 7,
wherein a first of the two or more comfort noise generation modes is a frequency domain comfort noise generation mode,
wherein a second of the two or more comfort noise generation modes is a linear prediction domain comfort noise generation mode,
wherein the selector (110) is configured to: if the previously selected generation mode is a linear prediction domain comfort noise generation mode and the current long term tilt value is greater than a first threshold, selecting a frequency domain comfort noise generation mode, wherein the previously selected generation mode was previously selected by the selector (110), and
Wherein the selector (110) is configured to: if the previously selected generation mode is a frequency domain comfort noise generation mode and the current long term tilt value is less than a second threshold, a linear prediction domain comfort noise generation mode is selected, wherein the previously selected generation mode was previously selected by the selector (110).
10. An apparatus for generating an audio output signal based on received encoded audio information, comprising:
a decoding unit (210) for decoding encoded audio information to obtain mode information encoded within the encoded audio information, wherein the mode information indicates an indicated comfort noise generation mode of two or more comfort noise generation modes; and
a signal processor (220) for generating the audio output signal by generating comfort noise according to the indicated comfort noise generation mode,
wherein a first of the two or more comfort noise generation modes is a frequency domain comfort noise generation mode.
11. The device according to claim 10,
wherein a second of the two or more comfort noise generation modes is a linear prediction domain comfort noise generation mode, an
Wherein the signal processor (220) is configured to: if the indicated comfort noise generation mode is a linear prediction domain comfort noise generation mode, the comfort noise is generated by using a linear prediction filter.
12. A system, comprising:
the apparatus (100) for encoding audio information according to one of the claims 1 to 9,
the apparatus (200) for generating an audio output signal based on received encoded audio information according to claim 10 or 11,
the selector (110) of the apparatus (100) according to one of claims 1 to 9, configured to: a comfort noise generation mode is selected from two or more comfort noise generation modes based on a background noise characteristic of the audio input signal,
the encoding unit (120) of the apparatus (100) according to one of claims 1 to 9, configured to: encoding the audio information to obtain encoded audio information, wherein the audio information comprises mode information indicating the selected comfort noise generation mode as the indicated comfort noise generation mode,
wherein the decoding unit (210) of the apparatus (200) according to claim 10 or 11 is configured to receive the encoded audio information and is further configured to decode the encoded audio information to obtain mode information encoded within the encoded audio information, and
The signal processor (220) of the apparatus (200) according to claim 10 or 11, wherein the signal processor is configured to: the audio output signal is generated by generating comfort noise according to the indicated comfort noise generation mode.
13. A method for encoding audio information, comprising:
selecting a comfort noise generation mode from two or more comfort noise generation modes according to a background noise characteristic of the audio input signal; and
encoding the audio information, wherein the audio information includes mode information indicating a selected comfort noise generation mode,
wherein a first of the two or more comfort noise generation modes is a frequency domain comfort noise generation mode.
14. A method for generating an audio output signal based on received encoded audio information, comprising:
decoding the encoded audio information to obtain mode information encoded within the encoded audio information, wherein the mode information indicates an indicated comfort noise generation mode of two or more comfort noise generation modes, and
generating the audio output signal by generating comfort noise according to the indicated comfort noise generation mode,
Wherein a first of the two or more comfort noise generation modes is a frequency domain comfort noise generation mode.
15. A computer readable medium storing a computer program for implementing the method according to claim 13 or 14 when executed on a computer or signal processor.
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| PCT/EP2015/066323 WO2016016013A1 (en) | 2014-07-28 | 2015-07-16 | Apparatus and method for comfort noise generation mode selection |
| CN202110274103.7A CN113140224B (en) | 2014-07-28 | 2015-07-16 | Apparatus and method for comfort noise generation mode selection |
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